The present disclosure relates to a drive device including a rotary electric machine and an inverter connected between the rotary electric machine and a direct-current power supply.
A device disclosed in Japanese Patent Application Publication No. 2007-166803 is known as such a drive device as described above. To control drive of a rotary electric machine (motor-generators MG1 and MG2) in such a device, the device needs to be provided with a current sensor for detecting a current flowing in a stator coil of each phase. The conventional current sensor used in the drive device generally uses a Hall element as shown in Japanese Patent Application Publication No. 2007-166803. The sensor using the Hall element has relatively stable temperature characteristics and can accurately detect the current, and hence, is often used to enable accurate drive control of the rotary electric machine in the drive device likely to be subjected to a high temperature environment. The sensor using the Hall element is, however, generally expensive, thereby contributing to an increase in cost.
In the case of, for example, electrical appliances, such as an air conditioner, techniques are known in which a shunt resistor provided in an inverter circuit is used to detect the current flowing in the stator coil of each phase of the rotary electric machine (Japanese Patent Application Publication No. 2011-125130, Japanese Patent Application Publication No. 2005-151790 and Japanese Patent Application Publication No. 2005-192358). The shunt resistor is inexpensive, and hence, the product cost can be lower than that in the case of structuring the rotary electric machine such that the current is detected by the sensor using the Hall element.
The shunt resistor is, however, lower in current detection accuracy and more susceptible to ambient temperature than the sensor using the Hall element. This may prevent desired accuracy from being ensured for the drive control of the rotary electric machine (such as the motor-generators MG1 and MG2 in Japanese Patent Application Publication No. 2007-166803) when the shunt resistor is used to simply reduce the product cost. In particular, in view of the fact that the installation environment of the drive device tends to be of considerably higher temperature than the installation environment of general electrical appliances, using the shunt resistor is liable to reduce accuracy of controlling the rotary electric machine. Hence, in the case of using the shunt resistor for current detection in the drive device, sufficient consideration is necessary as to in what form the shunt resistor is used.